Ophthalmoscope including therapy beam pulse information storage

ABSTRACT

An ophthalmoscope includes a therapy beam source configured to apply therapy beam pulses onto an eye and a drive unit configured to store information about the therapy beam pulses applied onto the eye.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.12/307,677, filed Jan. 6, 2009, which is a national phase application ofPCT/EP2007/056967, filed pursuant to 35 U.S.C. §371 on Jul. 9, 2007,which claims priority to EP06116853.0 filed on Jul. 7, 2006. Allapplications are incorporated herein by reference in their entirety andfor all purposes.

FIELD OF THE INVENTION

The present invention relates to an ophthalmoscope for examining apatient's eye.

BACKGROUND

An ophthalmoscope is used to observe the patient's eye background, forexample for retinal examinations. An ophthalmoscope delivershigh-resolution color or black-and-white images in continuoussuccession, so that it can be used to diagnose the eye as well as forcarrying out and documenting therapeutic interventions. Imaging of theeye background, for example the retina, constitutes an optical challengein this regard since both the illumination and the observation of theeye background is carried out through a comparatively small entry pupilof the eye. The eye background furthermore generally has only a weakreflectivity, which dominates for red color components, so thathigh-contrast color images of the eye background can in general beproduced only by a light source with strong blue and green components.

Optical examination of the eye background with the aid of anillumination beam, which is examined as an observation beam afterreflection for example from the retina, is moreover made difficult byundesired further reflections from the interfaces of the cornea as wellas by undesired light scattering for example from vitreous bodyturbidities. All these perturbing light beams, which may be contained inthe observation beam but are not attributable to the desired reflectionof the illumination beam from the part of the eye to be examined, willbe referred to together below as “stray light”.

In order to resolve this stray light problem, EP 1389943 B1 discloses anophthalmoscope for examining a patient's eye, comprising, anillumination device for generating an illumination beam, illuminationimaging optics for imaging the illumination beam onto the eye, and meansfor scanning the illumination beam over the eye, as well as anobservation device which comprises an electronic sensor with an array ofphotosensitive pixels, which can respectively be activated and/or readout in rows, observation imaging optics for imaging an observation beam,generated by reflection of the illumination beam from the eye, onto theobservation device, and means for excluding stray light from theobservation beam.

The illumination device used in this case is particularly a halogenlamp, the light of which is collimated by means of a condenser andfocused by the illumination imaging optics onto the patient's eyebackground. The observation beam reflected by the eye background isimaged by the observation imaging optics onto an image plane, in whichthere is a CCD sensor as an observation device.

The means for scanning the illumination beam over the eye in thisophthalmoscope according to the species are formed by a slit shutter,which oscillates in front of the halogen lamp in the illumination beamcollimated by the condenser. This shutter is made of an opaque material,for example a flat metal material and transmits only a linear segment ofthe illumination beam, which is defined by the size of the slit shutterand is likewise scanned to and fro over the patient's eye at thisoscillation frequency.

The means for excluding stray light from the observation beam in thisophthalmoscope according to the species are also formed by amechanically oscillating slit shutter. In particular, EP 1389943 B1proposes that the slit shutter oscillating in front of the halogen lampand the slit shutter oscillating in front of the CCD sensor, which inany event must be synchronised with one another for imaging reasons,should be formed as a shutter slit pair in a common metal sheet.

In practice, however, it has been found that particularly the selectionof a metal sheet which has a slit shutter and oscillates in front of thesensor leads to problems. This is because on the one hand theoscillations of the mechanical oscillator for the metal sheet can bedecoupled only insufficiently from the housing of the instrument, whichgenerally entails difficulties in handling the ophthalmoscope and inparticular degradations of the image sharpness owing to co-vibration ofthe sensor.

On the other hand, in order to achieve a maximally compact configurationof the ophthalmoscope, the shutter in the observation beam must lie asaccurately as possible in the image plane of the observation device andtherefore on the sensor. It is nevertheless compulsory to maintain acertain minimum distance of the metal sheet oscillating from the sensor,which inevitably leads to inferior suppression of perturbing straylight.

SUMMARY OF THE INVENTION

An ophthalmoscope includes a therapy beam source configured to applytherapy beam pulses onto an eye and a drive unit configured to storeinformation about the therapy beam pulses applied onto the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an ophthalmoscope of the prior art.

FIG. 2 is a schematic view of an ophthalmoscope according to anembodiment of the present invention.

FIGS. 3 a-3 c show plan views of arrays of photosensitive pixels of anelectronic sensor at three different times during a readout process.

FIG. 4 a shows a simplified time diagram describing the exposure timet_(INT) of a pixel row.

FIG. 4 b shows a simplified time diagram of a trigger signal at thestart of a readout process of the electronic sensor.

FIG. 5 shows a schematic view of an ophthalmoscope according to anotherembodiment of the present invention with line focusing optics and atiltably mounted mirror in the illumination beam.

FIG. 6 shows a schematic view of an ophthalmoscope according to anotherembodiment of the present invention with two observation beams forstereoscopic images.

FIG. 7 shows a schematic view of an ophthalmoscope according to anotherembodiment of the present invention for simultaneous examination of theeye foreground.

FIG. 8 is a schematic view of an ophthalmoscope according to anembodiment of the present invention supplemented with therapy functions.

FIGS. 9 a and 9 b are cross-sectional views of the pupil plane of thehuman eye when using the ophthalmoscope of FIG. 8.

FIG. 10 shows a time diagram which explains the functionality of theactivation of the targeting beam as a function of time in theophthalmoscope of FIG. 8.

FIG. 11 is a schematic view that represents the sequence, explained inthe time diagram of FIG. 10, in the image field.

FIG. 12 is a schematic view of an ophthalmoscope according to anembodiment of the present invention for the simultaneous measurement offluorescent emissions.

FIG. 13 is a schematic view of an ophthalmoscope according to anembodiment of the present invention, in which an additional light sourceis used to improve the fluorescent light measurement result.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the above described features.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of an ophthalmoscope 10 of theprior art for studying a patient's eye 12. The light emitted by anillumination device 14 is collimated by means of a condenser 16 andstrikes a slit shutter 18 which oscillates, specifically in a directionperpendicular to the optical axis A of the ophthalmoscope 10 in theplane of the drawing in the schematic representation of FIG. 1. Thisslit shutter 18 is oriented perpendicularly to the plane of the drawing.

A line, the length and thickness of which is defined by the shape of theslit shutter 18 and whose position depends on the current location ofthe oscillating slit shutter, is thereby extracted from the flat lightspot onto which the condenser 16 has collimated the light of theillumination device 14.

Using further lenses 20, 22, the illumination beam 19 is focused into anintermediate image plane B, from which it is imaged through anophthalmoscopic lens 24 onto the eye 12. The schematic representation ofFIG. 1 in this case shows imaging onto the eye background, for examplefor a retinal examination.

The observation beam, resulting from reflection of the illumination beam19 by the eye background, images the eye background through theophthalmoscopic lens 24 into the intermediate image plane B. Thisintermediate image is focused by means of the further lenses 22, 28 ontoa CCD sensor 30. Immediately before reaching the CCD sensor 30, theobservation beam 26 must in this case pass through a further slitshutter 32 which oscillates in front of the CCD sensor 30, synchronouslywith the slit shutter 18 in the beam path of the illumination beam 19.

With the aid of the slit shutter 32, this ensures that essentially onlythe desired observation beam 26 reaches the CCD sensor 30, while straylight is excluded. Such stray light may, for example, be attributable toreflections from the front side of the eye or scattering by vitreousbody turbidities of the eye 12.

It can be seen in FIG. 1 that the oscillating slit shutter 32 isarranged comparatively close to the CCD sensor 30. This is essential,since the suppression of perturbing scattered light will deterioratewith an increasing distance between the slit shutter 32 and the CCDsensor 30. The effect of this proximity, however, is that vibrations maybe transmitted from the oscillating slit shutter 32 onto the CCD sensor30, for example via a housing (not represented in the figures) of theophthalmoscope 10. This leads to fundamental problems in handling theophthalmoscope 10, and in particular it degrades the sharpness of theimage of the eye 12 delivered by the CCD sensor 30.

FIG. 2 shows a schematic representation of an ophthalmoscope 10according to an embodiment of the invention. According to the embodimentrepresented in FIG. 2, the ophthalmoscope 10 according to the inventiondiffers from that of the prior art in that an electronic sensor 34,which comprises an array of photosensitive pixels that can respectivelybe activated and/or read out in rows and can be driven individually bymeans of an electronic drive circuit, is provided in the observationbeam path 26 instead of the CCD sensor 30 and the slit shutter 32oscillating in front of it. The electronic drive circuit is arranged inthe electronic sensor 34 and is not represented in the figures.

The functionality of the electronic sensor 34 controlled by theelectronic drive circuit will be explained below with the aid of FIGS. 3a to 3 c:

FIGS. 3 a to 3 c show a schematic plan view of an array ofphotosensitive pixels of an electronic sensor 34, represented in asimplified fashion. In the simplified embodiment shown, this array ofphotosensitive pixels comprises 10 pixel rows in all, which are numbered1, 2, . . . , 10. Each pixel row in FIGS. 3 a to 3 c comprisestwenty-four pixels, which generate charges by means of photosensitiveelements as a function of the incident amount of the light. Each pixel36 is assigned its own amplifier electronics, which convert theelectrical charge generated in the pixel 36 into a respective voltagesignal. The functionality of such electronic sensors with so-called“active pixels”, in particular CMOS sensors, is known per se and willnot be further explained here.

With the aid of the electronic drive circuit provided in the electronicsensor 34, each pixel row can be switched to one of three operatingstates:

-   -   a) A deactivated mode in which the pixel row does not integrate        any charges despite the incidence of light, and does not        therefore generate a voltage signal; the pixel rows 2, 3, . . .        , 7 are in this deactivated mode in FIG. 3 a, which is indicated        by blank pixels 36 in these pixel rows.    -   b) An active mode in which incidence of light leads to the        generation of a continuously rising voltage signal; pixel rows        8, 9 and 10 are in this operating state in FIG. 3 a, which is        indicated by simple hatching of these pixel rows.    -   c) A readout mode in which a pixel row is read out, i.e. the        voltage signal built up in a certain preceding exposure time is        interrogated by the electronic drive circuit; the pixel row is        subsequently erased, i.e. the voltage signal is reset back to        the value zero. Only pixel row 1 is in this readout mode in FIG.        3 a, indicated by the dense hatching.

The readout process of the electronic sensor 34, controlled by theelectronic drive circuit, will be explained below with the aid of FIGS.3 a to 3 c, 4 a and 4 b:

At a start time t₁ indicated in the time diagrams of FIGS. 4 a and 4 b,the electronic drive circuit receives a trigger signal, for example aTTL signal, from an electronic control unit 38, for example a centralcontrol computer. The leading edge of the trigger signal represented inFIG. 4 b starts a complete readout cycle of the electronic sensor 34, bypixel row number 1 initially being switched from the inactive state tothe readout state and subsequently to the active state, i.e. incidenceof light leads to the build-up of a voltage signal in each pixel of thefirst pixel row. The first pixel row remains in this active state for anexposure time t_(INT), and is read out by the electronic drive circuitat a corresponding instant t₁ of the next readout cycle.

After an adjustable time delay Δt has elapsed following the start timet₁, the second pixel row is also read out and switched to the activestate, and so is the third pixel row after a further time delay Δt. Inthe case shown in FIG. 4 a, t_(INT)=3×Δt is selected so that the secondand third pixel rows are currently also in the active mode at theinstant t₄=t₁+t_(INT)=t₁+3×Δt when the fourth pixel row is read out andactivated, whereas the first pixel row is already deactivated.

After the first pixel row has been read out at the instant t₁ it isactivated, and the second pixel row, which was exposed for the timet_(INT) starting from the instant t₁ of the previous cycle, is read outafter a further time delay Δt i.e. at an instant t₂=t₁+Δt. In this way,the readout process respectively advances by one pixel row of theelectronic sensor 34 in time intervals corresponding to the time delayΔt, i.e. from pixel row number 1 through to pixel row number 10 in theexample shown in FIGS. 3 a to 3 c. The effect of selecting t_(INT)=3×Δtis that three neighbouring pixel rows, namely the pixel rows n−1, n−2and n−3, are active at the time when the n^(th) pixel row is read out.This defines the effective width of the electronic slit shutter which,so to speak, moves from top to bottom over the array of photosensitivepixels 36 in FIGS. 3 a to 3 c. It is necessary to ensure that thevoltage built up in a pixel row during the time t_(INT) is notinterrogated until the next cycle of the electronic readout, when thispixel row is switched to the readout mode.

The total time T needed for a full cycle corresponds to the product ofthe number N of pixel rows (in the example of FIGS. 3 a to 3 c, N=10)and the time delay Δt, i.e. T=N×Δt. By selecting the three parametersΔt, t_(INT) and N, the image repetition rate 1/T and the effective widthof the electronic slit shutter can therefore be adjusted more flexiblythan the corresponding parameters of a mechanically oscillating slitshutter 32 in the prior art according to FIG. 1.

The electronic control unit 38 is adapted to use the trigger signal,represented in FIG. 4 b, in order to synchronise the respectively activepixel rows with the movement of the slit shutter 18 in the illuminationbeam. At the instant t₁ for example (see FIG. 3 a), the pixel rows 8, 9and 10 are active. The instant t₁ must therefore be selected so that itcorresponds to a time when the slit shutter 18 lies at the lower turningpoint of its oscillating movement. The sequence of pixel row activationprocesses represented in FIGS. 3 a to 3 c and 4 a, from the top (in FIG.3 a, pixel row number 1 is read out and then immediately activated) tothe bottom (in FIG. 3 c, pixel row 10 is read out and thereuponimmediately activated), then takes place synchronously with a movementof the slit shutter 18 from top to bottom in FIG. 2.

Since, as shown in FIGS. 3 a to 3 c and 4 a, an electronic shutterconstantly travels from top to bottom over the pixel array according tothis “rolling shutter” principle, the only images of the electronicsensor 34 which are processed are those which correspond to a downwardmovement of the illumination beam 19 which is synchronous therewith.Those oscillation phases in which the slit shutter 18 in FIG. 2 movesupwards are not usable. For this reason, after a complete readout cycleof the electronic sensor 34, in which the voltage signals built up inthe individual pixel rows in the preceding cycle are read out, therelease of the next trigger signal by the electronic control unit 38 isdelayed until the slit shutter 18 has again reached its upper turningpoint.

A further improvement of the image of the eye 12 delivered by theelectronic sensor 38 may be achieved not only by synchronising thereadout start time t₁ with the upper turning point of the oscillatingslit shutter 18, but also by matching the downward movement of theelectronic shutter in FIGS. 3 a to 3 c with the corresponding downwardmovement of the slit shutter 18 in the illumination beam 19. If forexample the slit shutter 18 oscillates sinusoidally in the illuminationbeam 19, then its speed with which it travels through the illuminationbeam 18 will respectively be equal to zero at the upper and lowerturning points of the oscillation, whereas it reaches a maximum in themiddle between the two turning points. This may be taken into account inthe electronic sensor 34 by not selecting the time delay Δt to beconstant, in contrast to FIG. 4 a, but instead selecting it to begreater as a function of the respective pixel row at the upper and loweredges of the pixel array (for example in the region of pixel rows 1 and10) than in the middle of the pixel array (in the vicinity of pixel rows5 and 6).

This additional electronic outlay, which is entailed when wishing toadapt the movement of the “rolling shutter” of the electronic sensor 34to the movement of the mechanical slit shutter 18, may be avoided ifconversely the time sequence of the electronic shutter as represented inFIGS. 3 a to 3 c, 4 a and 4 b is retained and the movement of themechanical slit shutter is adapted thereto. For example, the electroniccontrol unit 38 may control a driver mechanism (not represented in thefigures) of the slit shutter 18 so that the slit shutter 18 executes akind of “sawtooth” trajectory, i.e. it is moved with a constant speedfrom its upper turning point to its lower turning point and issubsequently returned much more rapidly to its upper turning point.

Depending on the desired image repetition frequency, such a sawtoothmovement of an extended metal sheet, in which the slit shutter 18 isprovided, may however prove to be difficult.

In an embodiment of the ophthalmoscope 10 according to the invention asrepresented in FIG. 5, the generation of the illumination beam 19 istherefore also modified relative to the prior art according to FIG. 1,in the form of line focusing optics in order to facilitatesynchronisation with the electronic shutter in the electronic sensor 34:

In FIG. 5, components which correspond to those of the embodimentrepresented in FIG. 2 are provided with the same references. Inparticular, an electronic sensor 34 having the properties describedabove is also used to record the observation beam in the preferredembodiment according to FIG. 5.

In this embodiment, however, a point-like light source is used as theillumination device 14, for example a laser or the end of an opticalwaveguide. The light emerging from it is converted into a parallel beamof rays by a condenser 40 and is directed onto a cylinder lens 42.Arranged behind the cylinder lens 42 in the beam direction, there is atiltably mounted mirror 44 which reflects the illumination beam 19approximately parallel to the optical axis A in FIG. 5, leftwards in thedirection of the lens 22 which lies in the focusing plane of thecylinder lens 42. The cylinder lens 42 is in this case positioned sothat the line focus generated by it is oriented perpendicularly to theplane of the drawing of FIG. 5.

The mirror 44 is mounted tiltably on a scanning device 46, which isdriven by the electronic control unit 38 that simultaneously controlsthe electronic drive circuit of the electronic sensor 34. The electroniccontrol unit 38 is adapted to control the scanning device 46 so that itscans the illumination beam 19 over the eye 12 by rotating the mirror 44in the plane of the drawing of FIG. 5, synchronously with the movementof the electronic shutter in the electronic sensor 34. With thecontinuous linear downward travel of the electronic shutter as shown inFIGS. 3 a to 3 c, the mirror 44 may execute a sawtooth trajectory forexample by rotating it anticlockwise in steps starting from the positionshown in FIG. 5 and finally, as soon as the electronic shutter in theelectronic sensor 34 has reached the lower pixel row, for example pixelrow number 10 in FIG. 3 c, returning it quickly in the clockwisedirection to its starting position according to FIG. 5.

In practice, such a tiltably mounted mirror has a very small moment ofinertia, so that it can be used not only at high frequencies butgenerally in a large frequency range. The combination of such a mirrorwith a “rolling shutter” according to FIG. 5, which therefore allowsfree selection of the image repetition rate and external synchronisationwith the aid of the electronic control unit 38, therefore permitsoptimal adaptation of the illumination of the eye 12 to the respectivelydesired observation. Owing to the low inertia of the mirror 44,vibrations are almost entirely avoided in the ophthalmoscope 10according to the invention.

The use of a coherent light source, for example a laser, makes itpossible to generate a very narrow illumination slit. If a minimalelectronic slit width of a single pixel row is selected at the sametime, corresponding to a height of a pixel 36 of about 5 μm, then it ispossible to achieve confocal imaging perpendicularly to the extent ofthe slit and therefore to carry out three-dimensional examinations ofthe eye.

FIG. 6 shows a schematic representation of another embodiment of theophthalmoscope 10 according to the invention with two observation beams26 for stereoscopic images. The illumination beam path in this case liesoutside the plane of the drawing, and is not represented in FIG. 6. Twoadjacent electronic sensors 34 are provided in this embodiment, in orderto make stereoscopic recordings of the eye 12. The illumination beampath may be selected either as in FIG. 2, i.e. with a slit shutter 18which oscillates to and fro in front of an illumination device 14, or asshown in FIG. 5, i.e. with line focusing optics in the illumination beam19. The advantages of the present invention, namely the avoidance ofmechanical slit shutters mechanically oscillating, become particularlysignificant in the embodiment of FIG. 6 because correspondingophthalmoscopes 10 of the prior art with the facility of stereoscopicobservation require a total of three slit shutters oscillating, namelyone slit shutter in the illumination beam 19 and two slit shutters 32 inthe two observation beams which essentially are mutually parallel.Especially in stereoscopic ophthalmoscopes 10 of the prior art, thisleads to serious vibration problems which are avoided by the invention.

FIG. 7 shows another embodiment of the ophthalmoscope 10 according tothe invention with an additional imaging unit, which images the eyeforeground through the ophthalmoscopic lens 24 and a further lens 48onto a separate image sensor 50. The separate image sensor 50 ispreferably also an electronic sensor with active pixels, for example aCMOS sensor, as was described in detail above.

The beam paths of the eye background and eye foreground illumination areseparated by a beam splitter 52 in this embodiment, a pellicle beamsplitter preferably being employed.

The eye foreground is illuminated in this embodiment by a separate lightsource (not represented in FIG. 7), which is positioned directly infront of the eye and ideally emits in the infrared.

In other regards, the embodiment of FIG. 7 corresponds to that of FIG.2, i.e. with a mechanically oscillating slit shutter 18 in theillumination beam 19. Naturally, the line focusing optics explained withthe aid of FIG. 5 may nevertheless also be employed in the embodiment ofFIG. 7.

FIG. 8 shows another embodiment of the ophthalmoscope according to theinvention which, based on the embodiment of FIG. 2, has beensupplemented with therapy functions. To this end a further light source60 is provided, which generates a therapy light beam that is collimatedby means of a lens 62 and is coupled through a beam splitter 64 into thebeam path, coaxially with the principal axis of the ophthalmoscope. Thetherapy light beam is in this case deviated by two mirrors 61, which arerespectively mounted tiltably about an axis perpendicular to the planeof the drawing of FIG. 8 and an axis lying in the plane of the drawing.The electronic control unit 38 also contains a drive unit, whichcontrols the tilting movements of the mirrors 61 on the basis ofsetpoint values which a user can input by means of an interface 63, forexample a joystick.

FIG. 9 a shows a schematic cross-sectional representation of the pupilplane of a patient's eye in the case of using the ophthalmoscope of FIG.8. Here, reference 53 denotes the pupil of the eye 12, reference 54denotes the pupil of the illumination beam path, and reference 56denotes the pupil of the observation beam path. The position of thetherapy light beam additionally coupled in with the aid of the beamsplitter 64 is indicated by dashes in FIG. 9 a, and is denoted byreference 55. In accordance with the input of the therapy light beam inFIG. 8, the therapy light beam 55 lies centrally in FIG. 9 a (i.e. onthe principal axis of the ophthalmoscope 10 according to the invention).

As an alternative, the therapy light beam may also be coupled indecentrally with the aid of the mirror 61 and the beam splitter 64, forexample coaxially with the illumination beam path. The correspondingcross-sectional representation of the patient's pupil plane is shown inFIG. 9 b.

FIG. 10 shows a time diagram which explains the functionality of theactivation of the targeting beam as a function of time. The instant T₁represents the starting point of the shutter movement at one end of theimage field. It expediently corresponds to the instant t₁ explainedabove, at which the first pupil row of the electronic sensor 34 is readout. The instant T₁ is therefore also defined by the leading edge,represented in FIG. 4 b, of a square-wave pulse. After a time delay τ,which as described above may be calculated from the position of thetargeting beam spot in the image field (or by values connectedtherewith), the targeting beam is then activated at an instant T₂ for atime T_(p), which is in turn indicated in FIG. 10 by a square-wavepulse.

FIG. 11 represents the sequence, explained in the time diagram of FIG.10, in the image field. At the instant T₁, the shutters are at thestarting point of their movement. In FIG. 11, the starting point isrepresented as lying at the upper edge of the image field. The movementof the shutters takes place downwards over the image field starting fromthe instant T₁, which is indicated by an arrow in the movementdirection. At the instant T₂, the lower edge of the shutter of theophthalmoscope 10 according to the invention has reached that position(x, y) in the image field where the targeting beam spot lies. At thisinstant, the targeting beam is then activated for the time T_(p).Expressed another way, the shining of the targeting beam is restrictedto those short periods of time in which the shutters of theophthalmoscope 10 actually permit observation of the desired region ofthe eye. The targeting beam is switched off outside these short periodsof time, so that perturbing reflections are minimised. This pulsedtargeting beam is in turn synchronised with the shutters with the aid ofthe electronic control unit 38.

FIG. 12 shows another embodiment of the ophthalmoscope according to theinvention for measuring fluorescent emissions. A beam splitter 65, whichwavelength-dependently reflects a part of the light coming from theobject through a lens 66 onto a second sensor 68, is in this case fittedin the observation beam path. The beam splitter 65 simultaneouslyfunctions as a blocking filter for the fluorescence measurement. Thefiltering effect of the beam splitter may be improved by additionalfilters in transmission 67 and 69. The electronic control unit 38 inthis case contains a drive unit, which ensures that the sensors 68 and34 are read out synchronously and two images are therefore recorded atthe same time.

FIG. 13 represents a refinement of the embodiment of FIG. 12, in whichan additional light source 72 is used to improve the fluorescencemeasurement result. The light of this additional light source 72 iscollimated via a condenser 71 and is coupled into the illumination beampath through a beam splitter 70. The light source 72 emits light in awavelength range which lies outside the absorption and emission bands ofthe fluorescent dye.

The invention is not restricted to the embodiments presented asnonlimiting examples. For example, it is to be understood that theelectronic sensor 34 explained with the aid of FIGS. 3 a and 3 c maycomprise in practice more than a thousand pixel rows, rather than justthe ten pixel rows shown there for the sake of simplicity.

It is furthermore to be understood that the specific layout of the beampaths of the illumination beam 19 and the observation beam 26, or theobservation beams 26 in the case of stereoscopic images, may be variedby known optical elements. It is likewise to be understood that furtherlight beams may be coupled into the proposed beam paths, for example fortherapeutic or diagnostic purposes, as is known in principle from theprior art.

In all these modified embodiments, the invention offers not only theabove-explained advantages of significantly reducing or entirelyeliminating mechanical vibrations due to slit shutters oscillating, butalso many other advantages:

-   -   a) As already emphasized, the electronic shutter of the        electronic sensor 34 lies in its image plane, so that the        exclusion of stray light is optimized.    -   b) Continuous imaging methods demand a sufficiently high image        repetition frequency of more than 10 Hz, in order to generate a        fluid impression of movement for the observer. The slit shutters        used in the prior art therefore have to oscillate with a high        frequency, which in practice can be achieved only by a        mechanical oscillator in resonance. This in turn demands exact        and extremely sensitive tuning, to within small margins, of the        natural frequency of the oscillator with the image repetition        frequency of the CCD sensor 30. The image repetition frequency        is therefore fixed for a given oscillator. In the ophthalmoscope        10 according to the invention, however, particularly in the        embodiment according to FIG. 5 which functions without any        mechanical slit shutter oscillating, there is no such        restriction due to a resonance condition.    -   c) In the ophthalmoscope of the prior art, the slit width for a        given mechanically oscillating shutter cannot be varied. Many        applications, however, require finely graded variation of the        slit width and therefore the effective exposure time. For        example, variation of the slit width or the image repetition        frequency, and therefore the effective exposure time, is        desirable to accommodate a wide variety of applications: in        angiography of the eye background it is necessary to detect the        weak fluorescent emission of a dye, which requires as long an        exposure time as possible. This is readily possible by adjusting        the parameters of the electronic sensor 34, in particular the        parameters N, Δt and t_(INT).    -   d) In the ophthalmoscope of the prior art, the frequency of the        oscillator for driving the slit shutter is in practice a        multiple of the image repetition frequency of the CCD sensor,        since mechanical oscillators with a low frequency on the one        hand cannot be tuned accurately in their oscillation frequency,        and on the other hand they lead to particularly inconvenient        vibrations of the entire equipment. This causes double exposures        on the CCD sensor 30 and therefore image blurring and motion        artefacts due to rapid movement of the eye 12 or other objects        being examined. The use of image sensors that combine two image        half frames, which are recorded at different instants, to form a        full image frame (interlacing) according to one of the        conventional video standards (PAL, NTSC), has proven        particularly disadvantageous. The further computer-assisted        processing and evaluation of the images (for example determining        the position, size, shape etc. of blood vessels in the eye 12)        is made difficult by such motion artefacts or interlacing        artefacts. The inventive avoidance of the mechanical slit        shutter in front of the sensor resolves all these problems.    -   e) The mechanical oscillator oscillating in resonance to drive        the slit shutters in the ophthalmoscope according to the prior        art generally performs a sinusoidal movement. The amount of        light integrally striking the eye 12 through the oscillating        shutter during a period is therefore distributed nonuniformly        over the eye 12, and this leads to a nonuniform contrast and        brightness distribution in the image. In order to obtain uniform        illumination of the image section despite this, the amplitude of        the oscillation is often increased to such an extent that only        the approximately linear component of the shutter trajectory        lies in the field of view. Only a fraction of the light incident        on the eye 12 is therefore used for the imaging, however, which        leads to a reduction in the sensitivity of the ophthalmoscope        10. In the ophthalmoscope 10 according to the invention,        conversely, the available light is utilised much better.    -   f) When using a conventional light bulb or a halogen lamp, which        uniformly illuminates the image plane of the illumination beam        path, the available luminance of the illumination device 14 is        utilised only inefficiently. The thermal radiation of the        illumination device 14 leads to a further difficulty in handling        the equipment. This problem can be avoided in the embodiment        shown in FIG. 5 by a laser and line focusing optics.    -   g) A halogen lamp, as is used in the prior art, emits a broad        thermal frequency spectrum whose maximum lies in the infrared        range, and which falls off at shorter wavelengths. Such a light        source is therefore unsuitable for generating a high-contrast        color image of the eye background, since the eye background        reflects primarily in the red spectral range.        Semiconductor-based image sensors are furthermore more strongly        sensitive in the red and infrared spectral ranges than at        shorter wavelengths. A color image of the eye background,        recorded with halogen illumination, therefore has a dominant red        channel but only weakly pronounced green and blue channels. The        image is therefore noisy and low in contrast. Although the use        of filters to influence the illumination spectra does improve        the color impression, it nevertheless greatly reduces the        luminance of the light source. For the aforementioned        observation of fluorescent emissions, however, intense        excitation of the dyes in a narrow spectral range is necessary.        This may be achieved in the embodiment according to FIG. 5 by        modern light sources, for example LEDs or lasers.

The use of such an electronic sensor in an ophthalmoscope makes itpossible to replace the mechanical shutter employed in the prior art bya so-called electronic shutter (“rolling shutter”). This is because withthe aid of the electronic drive circuit, all the pixel rows of such asensor can be activated, deactivated and read out simultaneously in acontrolled way. When a pixel is in the activated state, incidence oflight leads to the continuous generation of charges which are convertedinto a voltage signal in a CMOS sensor by means of the amplifierelectronics assigned to the respective pixel. Such build-up of voltageis however prevented in the deactivated state, and the pixel or even theentire pixel row is “switched off”.

By deliberately activating at least one pixel row in a particular regionof the array of photosensitive pixels and simultaneously deactivatingall the other pixel rows, the same result as with the aid of amechanical slit shutter can therefore be achieved electronically. In theophthalmoscope according to embodiments of the invention, stray lightcan therefore be excluded from the observation beam without thisrequiring a mechanically oscillating metal sheet with a slit shutter infront of the observation device. Furthermore, in contrast to themechanical shutter, the electronic shutter provided in accordance withthe invention lies not in front of but in the image plane of theobservation device, which improves the suppression of stray light.

The electronic drive circuit is adapted respectively to read out asingle row. An extremely fine resolution of the electronic sensor can beachieved in this way, which corresponds to a height of about 5 μm withtypical CMOS sensors. It would nevertheless in principle be conceivableto combine a plurality of pixel rows, in particular neighboring pixelrows, with the aid of the electronic drive circuit, i.e. always toactivate, deactivate or read them out together, and therefore improvethe luminous efficiency at the cost of the resolution.

The electronic drive circuit is adapted to change the current pixel rowto be read out, in particular from one pixel row to a neighboring pixelrow, respectively after an adjustable time delay (Δt) has elapsed. In analternative embodiment, in which immediately neighboring pixel rows areread out successively, the electronic drive circuit therefore requires atotal time T=N×ΔT for a complete cycle, i.e. full readout of theelectronic sensor with N pixel rows. The parameter N, which describesthe number of pixel rows of the sensor, may in this case be reduced froman upper limit dictated by the design of the sensor by using theabove-described electronic combination of neighboring pixel rows, whileat the same time the time delay parameter ΔT may be freely adjusted bythe operator of the ophthalmoscope according to the invention. The totaltime required for a full readout cycle may in this way be adjusted,according to the setting of the oscillation period or the oscillationfrequency of the mechanical slit shutter provided in the ophthalmoscope.

In one embodiment of the invention, the electronic drive circuit isfurthermore adapted to activate each pixel row for an adjustableexposure time (t_(INT)) before it is read out. The effect achievable bysetting this exposure time t_(INT) as a multiple of the time delay ΔT istherefore that each pixel row is exposed for a longer time, during whichit approaches the pixel row currently to be read out. In this way, theeffective width of the electronic slit shutter can be adjusted flexibly.

Expediently, the electronic drive circuit is adapted to start thereadout process in response to an external trigger signal. In this wayit is possible to ensure the synchronization of the shutter for theobservation device with the means for scanning the illumination beam.For example, a central control computer for the ophthalmoscope accordingto the invention may control on the one hand the electronic drivecircuit of the electronic sensor with the aid of this trigger signaland, on the other hand, a driver for a mechanical slit shutter in theillumination beam.

In principle, synchronization of the electronic shutter in theobservation beam with a mechanical shutter in the illumination beam mayreadily be achieved with the aid of such a central control computer. Thecentral control computer may of course also be part of the electronicsensor or part of the illumination device.

Moreover, the means for scanning the illumination beam over the eye maycomprise a tiltably mounted mirror with a scanning device. In order toensure that the illumination beam striking the tiltably mounted mirroralready has the desired line shape, either the ophthalmoscope accordingto the invention may furthermore comprise a fixed slit shutter forextracting a linear illumination beam or it may furthermore compriseline focusing optics for focusing the illumination beam in a line, inwhich latter case the line focusing optics expediently comprise acylinder lens. The use of such a tiltably mounted mirror, which isdriven with the aid of a galvanometer drive and is employed in anophthalmoscope in order to scan an illumination beam delivered by linefocusing optics, is also described in U.S. Pat. No. 6,758,564 B2 towhich reference is made in this regard.

For central control of the components of the ophthalmoscope according tothe invention, it is expedient that the electronic control unit shouldbe adapted to control the electronic drive circuit of the electronicsensor and the scanning device of the tiltable mirror. By transmittingthe aforementioned trigger signal to the electronic drive circuit of theelectronic sensor, the electronic control unit may then ensure that, forexample with a sinusoidally oscillating mirror, the readout process inthe electronic sensor begins at a suitable time, for example by readingout the upper pixel row of the electronic sensor as soon as theoscillating mirror has reached its upper turning point.

In this refinement of the ophthalmoscope according to the invention, theelectronic control unit is adapted to control the scanning device andthe electronic drive circuit so that the illumination beam is scannedover the eye synchronously with the change of the pixel row currently tobe read out. For example, the electronic control unit may impart asawtooth trajectory to the scanning device, which corresponds exactly tothe movement of the electronic slit in the electronic sensor.

For particularly precise examinations of the patient's eye with aparticularly high spatial resolution, it is proposed that the thicknessof the line of the focused illumination beam should correspond to theheight of the pixel row of the electronic sensor. Confocal imaging ofthe eye is thereby achieved, so that three-dimensional information aboutthe observed object can be obtained.

When using the said line focusing optics, the illumination device mayexpediently be a laser. As an alternative, any other form of anessentially point-like illumination device may be used, for example oneend of an illuminated optical waveguide.

According to one refinement of the invention, the observation devicecomprises two electronic sensors for stereoscopic examination of theeye. The advantages of the invention become particularly significant insuch an embodiment, since stereoscopic observation with two observationdevices in the prior art in fact requires a total of three slit shuttersoscillating, which according to the invention may be obviatedsubstantially or even entirely by using the line focusing optics.

Furthermore, according to another embodiment of the invention, theophthalmoscope comprises a separate light source and a separate imagesensor for examining the eye. In particular, with the aid of theillumination device, the illumination imaging optics, the observationimaging optics and the observation device, it is in this case possibleto examine the eye background, for example the retina of the eye, whilethe additional imaging unit is used to examine the eye foreground. Thismay be utilized both for medical examination of the eye foreground perse and for automatic positioning of the patient's eye, as well as fortracking the eye movements of the entire eye with the aid of informationwhich, for example, is obtained by reflection of a light beam from theeye foreground. In particular when adding up the eye background imagesfor angiography, it is advantageous that eye movements which haveoccurred between the individual images of the eye background can beestablished by means of such simultaneous observation of the eyeforeground.

The ophthalmoscope according to the invention may advantageously besupplemented with therapy functions. An important form of therapy in eyemedicine for the treatment of diseases such as diabetic retinopathy orage-related macular degeneration, is the thermal action by light ontissue regions to be treated, for example photodynamic therapy (PDT),photocoagulation of tissue or modern methods such as selective retinatherapy (SRT) and therapy below the coagulation threshold (sub-thresholdtherapy, STT). In all these forms of therapy, an intense light pulse isfocused onto a special zone of the retina. When carrying out thetherapy, it is necessary to ensure that important zones of the eyebackground (for example the macula) are not inadvertently damaged.

For this type of therapeutic intervention, besides a live image of theeye background, the treating doctor therefore also requires very precisecontrol of the position of the therapy light beam. A targeting beam istypically superimposed coaxially on the therapy light beam as an aid forpositioning the therapy light beam. This is always visible to thedoctor, but it has a different wavelength and a much lower intensitythan the therapy light beam and it does not therefore lead tomodifications of the eye background. Reflections from the variousinterfaces of the eye, which are generated by the light source forilluminating the eye background as well as by the targeting beam, dohowever make control much more difficult.

An ophthalmoscope which generates a reflection-free live image of theeye background and simultaneously projects a therapy beam, on which atargeting beam with a different wavelength is generally superimposed,onto the eye background, constitutes an important instrument for eyemedicine. It allows the doctor to be assisted by a computer, for examplefor navigation over the eye background in order to position thephotocoagulation point. Such computer assistance is already prior art inother fields of medicine (for example minimally invasive surgery orneurosurgery). In eye medicine, its implementation has previously beenprevented by the lack of observation and treatment instruments. Thepresent invention can remedy these technical deficiencies.

The therapeutic intervention may furthermore be documented objectivelyby computer assistance. To date this has been possible onlyapproximately, for example with the retina being heated by the lightpulse during photocoagulation so as to cause a permanent and clearlyvisible modification of the tissue. The effect of this is that thedestroyed tissue areas, and therefore the loss of vision after thetherapy, are usually much greater than is medically necessary. Moderntreatments such as PDT, SRT and STT are specifically intended to avoidsuch visible damage to the retina. Without the documentation method madepossible by the present invention, quality assurance is not possible forthese therapies.

A slit lamp, onto which a photocoagulation laser is adapted withcorresponding input optics, is typically used for treatment of theretina with intense light pulses. A slit lamp is a stereomicroscope withvariable slit illumination, the microscope as well as the illuminationbeing mounted rotatably about a common axis in a plane.

In order to observe the eye background, the user holds anophthalmoscopic lens or a contact glass by hand in front of or on thepatient's eye. The therapy laser system usually consists of the coaxialcombination of a targeting beam and a therapy beam, which expedientlyhave different wavelengths in order to make it easier to distinguishthem. The therapy beam is generally input coaxially with the observationbeam path between the microscope and the ophthalmoscopic lens.

It is therefore inevitable that particularly the targeting beam willgenerate strong reflections at the various interfaces between the slitlamp and the eye background, which will be seen as interference by theobserver. These reflections are very much brighter than the lightreflected by the eye background, and the observer can only move them tothe edge of the image field laboriously by skilful movement/alignment ofthe microscope and the ophthalmoscopic lens, or else the observer mustsimply tolerate them. In principle, reflections from interfaces of thehuman eye cannot be avoided by technical means (i.e. by blooming thesurfaces).

However, the said reflections of the targeting beam not only hinder thework of the operator looking through the eyepiece of the microscope, butmay also compromise or prevent the use of systems which record images ofthe eye background with the aid of electronic sensors and which areintended to aid the user during the therapy by computer-assistedevaluation.

In another embodiment, the present invention alleviates the existingrestrictions/disadvantages of the prior art by providing a device forprojecting a targeting beam and a therapy beam, which also allowsreflection-free observation of the eye background by the targeting beamprojected onto it. A targeting beam that does not need to be polarizedis used, which reduces the costs for the light sources and the opticsbeing employed. Reflections which may be caused by the targeting beamare fully suppressed. Only a single detector is required in this casefor tracking the targeting beam on the object.

In the present invention, the therapy beam, with the targeting beamsuperimposed on it, is coupled into the beam path of the instrument withthe aid of a beam splitter. The therapy beam may in this case bearranged coaxially with the illumination beam path or coaxially with theprincipal axis of the instrument. It must not however be coaxial withthe observation beam path since this conflicts with the principle ofsuppressing reflections which is employed, based on separating the beampaths in the pupil plane of the eye. The effect of separating the beampaths is that the image of a reflection due to the targeting beam at anoptical interface between the sensor and object planes is not formed atthe same position on the sensor as the image of the targeting beam spotgenerated on the object (here: the eye background).

The beam splitter may expediently be rendered highly reflective for thewavelength of the therapy beam, but partially transparent for thewavelength of the targeting beam. In this way, only light of thetargeting beam reaches the detector and light of the therapy beam doesnot. As an alternative, the beam splitter may be configuredwavelength-independently and an additional selective filter may be usedin the observation beam path, which suppresses the light of the therapybeam. Undesired reflections and stray light, which are due to thetargeting beam, are suppressed by operating the targeting beam inpulses.

Considering a fixed point on the object, onto which the targeting beamis directed, the targeting beam is only switched on for the time T_(p)exactly at the instant T₂ when the observation shutter of the confocalimaging system is passing over precisely this object point. Theactivation of the targeting beam is synchronized with the confocalshutter arrangement by a drive unit. This drive unit has informationabout the respective position of the targeting beam spot on the objectand about the start time of the shutter movement. This drive unit ispreferably the same as the drive unit which synchronizes theillumination and observation shutter movements.

This may for example be achieved by the drive unit receiving an analogueor digital position signal of the control mirror of the targeting beamand a synchronization pulse of the shutter movement. The position of thetargeting beam spot on the object may, for example, be known a priorifrom the position of one or more deviating mirrors which determine theangular excursion of the targeting beam. From the position (x, y) of thetargeting beam and the speed v of the shutter movement, it is possibleto calculate a time delay τ=y/v (for movement of the shutter in the ydirection) between the start time of the shutter movement and theactivation of the targeting beam, and to convert this into acorresponding, expediently square-wave pulse sequence. When thetargeting beam moves on the object, the time delay is adapted accordingto the position.

The device according to embodiments of the invention imposes minimalrequirements on the therapy and targeting beam sources being used. Thesources employed need not necessarily be polarized and the pulseoperation, which takes place according to the invention on a timescaleof 100 μs-10 ms, is known per se.

In another advantageous embodiment of the invention, a drive unit isused which evaluates the images recorded by the instrument according tothe invention with the sensor, particularly in real-time. This driveunit performs one or more of the following functions:

-   -   Detecting or determining a coordinate system which is stationary        on the object, i.e. object-referenced, with the aid of        structures on the object in the images recorded by the device        according to the invention, or on images of the same object        which have been recorded by other devices,    -   Determining the position of the targeting beam in this        object-referenced coordinate system,    -   Positioning the targeting beam spot on the eye background        according to instructions by the user via a suitable interface        (for example a joystick), using one or more suitable deviating        mirrors which the drive unit can adjust,    -   Positioning the targeting beam spot without direct intervention        by the user, using one or more suitable deviating mirrors which        the drive unit can adjust,    -   Enabling or preventing the triggering of a therapy beam pulse,    -   Controlling the parameters of the therapy beam pulse (for        example the pulse duration, pulse repetition rate, light power        etc. in the case of photocoagulation),    -   Measuring the duration, intensity and frequency of the therapy        light pulses,    -   Storing the control parameters of the therapy light pulses and        storing the measured values.

By performing these functions, the following methods are possible inconjunction with a suitable display (for example a monitor screen):

-   -   The user defines regions (zones) in the object-referenced        coordinate system on the object, where the application of        therapy light pulses is generally permitted or generally        prevented by the drive unit. This may be done with the aid of a        single image previously recorded by the equipment according to        the invention, or by using images from other equipment according        to the prior art. To this end, the drive unit determines in        real-time the position of the targeting beam in the        object-referenced coordinate system and compares the position        with the predetermined regions, and as appropriate enables or        prevents the triggering of a therapy light pulse. In another        embodiment, the drive unit carries out the definition of the        aforementioned zones automatically by analyzing the image.    -   The drive unit superimposes information onto the display of the        live image, the transformations of the position of the        superimposed information being compensated for relative to the        live image, i.e. both the position of the superimposed        information and the live image are based on the same        object-referenced coordinate system. The superimposition may be        carried out by a rapid image change or by contrast-based        overlaying. The information may for example consist of images of        the object, which have been recorded at an earlier time or by        using different imaging methods with another instrument, or        graphical representations compiled by the user in the object        coordinate system at a different time.    -   The user establishes one or more positions, where a therapy        light pulse is intended to be applied, in the object-referenced        coordinate system on a reference image (target positions). The        drive unit then assists the application of a therapy light pulse        onto a predetermined position in the object-referenced        coordinate system of the object.        -   While the user is adjusting the position of the targeting            beam manually, the drive unit displays the target position            in the object-referenced coordinate system as superimposed            information in the live image.        -   The drive unit enables the triggering of a therapy light            pulse whenever the user has steered the targeting beam onto            the target position with an accuracy established a priori.        -   The drive unit automatically triggers a light pulse whenever            it has steered the targeting beam automatically onto the            target position in the object-referenced coordinate system.    -   The drive unit generates a pattern of two or more targeting beam        spots on the eye background by moving and activating the target        in a suitable way synchronized with the movement of the        observation shutter. The position of the pattern on the eye        background is determined by the user via an interface, or is set        automatically by the drive unit without intervention from the        user. The triggering of the therapy light pulse then takes place        at the positions of the pattern generated by the targeting beam.        Application of therapy light pulses in such patterns increases        the regularity of the pulse placement on the eye background and        therefore the reproducibility of the therapy result. In another        embodiment of the invention, a pattern is not generated        physically on the eye background, but is merely superimposed        virtually on the displayed live image. The movement of the        virtual pattern is in this case coupled with the movement of the        targeting beam spot on the eye background.    -   The drive unit performs stabilization of the live image with        respect to the coordinate system of the object and the display,        i.e. the object coordinate system is kept fixed with reference        to the coordinate system of the display.    -   The drive unit performs stabilization of the targeting beam spot        in the object coordinate system, i.e. the drive unit moves the        targeting beam in a suitable way so that it executes the same        relative movements as the object.    -   The drive unit carries out simultaneous stabilization of the        live image with the coordinate system of the display and        stabilization of the targeting beam spot in the object        coordinate system.    -   While a therapeutic measure is being carried out by means of the        therapy light beam, the drive unit stores the intervention sites        (the coordinates in the object-referenced coordinate system        where light pulses have been applied) and the parameters of the        therapy light pulses (such as pulse duration, light power etc.),        so that this information can be displayed at any time by once        more superimposing the stored information on live or static        images, even when there are no visible traces of the action of        light on the object.    -   After application of a therapy light pulse, the drive unit        evaluates either the reflectivity of the tissue at the position        of the therapy light action by means of image processing, or        another measurement value which is correlated with the        temperature of the tissue during the therapy light pulse action        and therefore the therapeutic effect, and it modifies the        parameters of the therapy light source in a suitable way for the        next therapy light pulse. In another embodiment, the evaluation        is carried out by means of image processing or the evaluation of        a suitable measurement value during the application of a therapy        light pulse, and it terminates the therapy light pulse action as        soon as a desired status of the tissue is reached.

In addition or as an alternative to the therapy functions describedabove, the ophthalmoscope according to embodiments of the invention maymoreover be extended with a view to carrying out fluorescencemeasurements as will be explained below.

Besides generating simple color images of the retina, ophthalmoscopesare also used for more complex imaging methods, for example qualitativedetection of the fluorescence of a dye which has been introduced intothe patient's bloodstream, in the vessels of the retina. The particularchallenge in this field consists in detecting the weak fluorescence byoptics whose geometrical optical flux is limited by the specialconditions when observing the eye background. A particular difficultyconsists in detecting the fluorescence of dyes (for example lipofuscin)naturally present in the human eye and their spatial distribution, theconcentration and therefore the luminosity of which dyes afterfluorescent excitation is generally very low.

In general, two filters are used for a fluorescence measurement with abroadband light source: an excitation filter for the illumination and ablocking filter for the observation. When a narrowband light source isused (for example a laser, LED), the excitation filter may be obviated.The transmission curves of the filters are configured so that theirmaximum transmission coincides with the maxima of the absorption oremission curves of the dyes. At the same time, however, the blockingfilter must efficiently suppress all of the excitation light in order toobtain a high signal-to-noise ratio.

The fluorescent signal of an object is generally orders of magnitudeless than, for example, the excitation light scattered by the objectaccording to Lambert's law. A weak measurement signal entails the needfor expensive and sensitive sensors, which therefore necessarily have alow resolution. On the other hand, especially in the field of eyemedicine, the incidence of a light onto the object cannot be increasedarbitrarily, rather there are critically low limit values precisely atshorter visible wavelengths.

The conventional method of increasing the signal-to-noise ratio in imageprocessing, by averaging a plurality of images (measurements), cannot begenerally employed in eye medicine since the object, i.e. the human eye,moves during the observation. Registering a plurality of images insuccession, i.e. determining the transformations which have taken placebetween individual images of a series of images, could allow averaging.For the special application of fluorescence measurement in the humaneye, however, the use of such technology is not possible since thefluorescent images are not very pronounced and are very noisy, owing tothe weak signal.

The refinement of the invention as proposed here is particularlysuitable for compiling fluorescence measurements of the eye background,since it expediently makes it possible to average possibly very noisyimages of moving objects. In a fluorescence measuring device accordingto the prior art, the majority of the light coming from the object to beobserved is absorbed or reflected by the blocking filter.

In an advantageous embodiment of the invention, the light of theexcitation light source is used to improve the measurement signals. Tothis end a dichroic beam splitter, which splits the light coming fromthe object into the shortwave component of the excitation light and thelongwave component of the fluorescent emission, is fitted into theobservation beam path. The reflected light is in this case imaged ontoan additional sensor.

The sensors are operated in a chronologically synchronized fashion, i.e.they function with the same image repetition frequency and they startthe integration time of an image at the same instant. Chronologicallysynchronous image pairs can therefore be recorded. The fluorescent imageis in general poorly pronounced in this case, while the image of thescattered excitation light is substantially more pronounced. It istherefore comparatively easy for the geometrical transformations, whichhave resulted from the movements of the object between the individualimages of a series of images, to be calculated from the image of theexcitation light. The inverse transformations are then applied to thefluorescent images, so that these can be averaged by addition. Ideally,the signal-to-noise ratio can be improved by a factor of √{square rootover (2)} with each image pair by this method.

Another advantageous embodiment of the invention uses the light of anadditional light source, which emits in a wavelength range that liesoutside the absorption and emission bands of the fluorescent object.This additional light source is expediently coupled into theillumination beam path. A dichroic beam splitter which splits the lightcoming from the object into the shortwave component of the excitationlight and the light of the additional light source on the one hand, andthe longwave component of the fluorescent emission on the other hand, isnow fitted into the observation beam path.

The use of an additional light source offers the advantage that,irrespective of the requirements of the fluorescence measurement, thewavelength may be freely selected outside the absorption and emissionbands and expediently selected in a wavelength range which allowsstronger exposure of the eye. The images which are used to determine thegeometrical transformations are more pronounced owing to the high lightintensity, so that the averaging of the fluorescence measurements can becarried out more accurately.

What is claimed is:
 1. An ophthalmoscope comprising: an illumination device configured to direct an illumination beam onto a background of an eye; an observation device configured to image an observation beam reflected by the eye background onto an image plane; a photosensitive electronic sensor disposed in the image plane and configured to generate a live image of the eye background; a therapy beam source configured to apply therapy beam pulses onto the eye background; and an electronic drive unit, including a computer, operatively coupled to the sensor and configured to evaluate the live image of the eye background in real-time and determine an object-based coordinate system of the eye background based on structures of the eye in the live image, the object-referenced coordinate system being stationary relative to the eye background, wherein the electronic drive unit is further configured to measure positions of the therapy beam pulses, projected through the pupil onto the eye background, relative to the object-referenced coordinate system and store information about the therapy beam pulses applied onto the eye background, the information including the positions of the therapy beam pulses on the eye background.
 2. The ophthalmoscope of claim 1, wherein the drive unit is configured to store parameters characterizing the therapy beam pulses applied onto the eye, wherein the parameters include a pulse duration, a light power, a wave length and/or a spot size of the therapy beam pulses.
 3. The ophthalmoscope of claim 1, wherein the drive unit is configured to store the information about the therapy beam pulses immediately before, during, or after the application of the therapy beam pulses.
 4. The ophthalmoscope of claim 1, further comprising: a display configured to display the live image and/or a static image of the eye, wherein the drive unit is configured to superimpose the stored information onto the live image and/or the static image to display the stored information.
 5. The ophthalmoscope of claim 4, wherein the drive unit is configured to use the same object-referenced coordinate system as a basis for both the live images of the eye and the positions of the information being superimposed onto the live images.
 6. The ophthalmoscope of claim 5, wherein the drive unit is configured to fix the object-referenced coordinate system with respect to a coordinate system of the display of the ophthalmoscope to stabilize the live images.
 7. The ophthalmoscope of claim 4, wherein the drive unit is configured to superimpose the live images with an image of the eye, and wherein the image of the eye is recorded at an earlier time and/or by using different imaging methods with another instrument, and/or with graphical representations compiled by the user in the object-referenced coordinate system at a different time.
 8. The ophthalmoscope of claim 1, wherein the drive unit is configured to use the same object-referenced coordinate system as a basis for both the live images of the eye and the positions of the information being superimposed onto the live images.
 9. The ophthalmoscope of claim 8, wherein the drive unit is configured to fix the object-referenced coordinate system with respect to a coordinate system of the display of the ophthalmoscope to stabilize the live images.
 10. The ophthalmoscope of claim 1, wherein the drive unit is configured to superimpose the live images with an image of the eye, and wherein the image of the eye is recorded at an earlier time and/or by using different imaging methods with another instrument, and/or with graphical representations compiled by the user in the object-referenced coordinate system at a different time.
 11. The ophthalmoscope of claim 1, wherein the drive unit is configured to control the therapy beam source by adjusting parameters characterizing the therapy beam pulses, wherein the parameters include a pulse duration, a pulse repetition rate, and/or a light power.
 12. The ophthalmoscope of claim 11, wherein the drive unit is configured to modify the parameters of the therapy beam source for subsequent applications of therapy beam pulses based on tissue reflectivity.
 13. The ophthalmoscope of claim 11, wherein the drive unit is configured to terminate the application of therapy beam pulses as soon as a desired status of tissue is reached.
 14. The ophthalmoscope of claim 1, wherein the drive unit configured to store and/or evaluate a reflectivity of tissue of the eye at positions of therapy pulse action by means of image processing, or another measurement value that is correlated with a temperature of tissue during the therapy beam pulse action.
 15. The ophthalmoscope of claim 14, wherein the drive unit is configured to modify the parameters of the therapy beam source for subsequent applications of therapy beam pulses based on the tissue reflectivity or the other measurement value.
 16. The ophthalmoscope of claim 14, wherein the drive unit is configured to terminate the application of therapy beam pulses as soon as a desired status of tissue is reached.
 17. A method for using an ophthalmoscope, the method comprising: focusing an illumination beam onto a background of an eye; imaging an observation beam reflected by the eye background onto an image plane; generating a live image of the eye background with a sensor disposed in the image plane; applying therapy beam pulses onto the eye background; and evaluating the live image of the eye background in real-time; electronically determining, using a computer, an object-based coordinate system of the eye background based on structures of the eye, the object-referenced coordinate system being stationary relative to the eye background; measuring positions of the therapy pulses, projected through the pupil onto the eye background, relative to the object-referenced coordinate system; and storing information about the positions of the therapy beam pulses applied onto the eye background.
 18. The method of claim 17, and further comprising: storing parameters characterizing the therapy beam pulses applied onto the eye, wherein the parameters include a pulse duration, a light power, a wave length and/or a spot size of the therapy beam pulses.
 19. The method of claim 17, and further comprising: storing the information about the therapy beam pulses immediately before, during, or after the application of the therapy beam pulses.
 20. The method of claim 17, further comprising: displaying the live image and/or a static image of the eye; and superimposing the stored information onto the live image and/or the static image to display the stored information. 